JPS58221803A - Antireflection film for potassium chloride - Google Patents

Abstract

PURPOSE:To improve the optical characteristics and water resistance by successively forming an arsenic trisulfide (As2S3) film, a lead fluoride (PbF2) film and an arsenic trisulfide film on the surface of a potassium chloride (KCl) substrate. CONSTITUTION:The 1st As2S3 film 1 having 2.38 refractive index n1, a PbF2 film 2 having 1.55 refractive index n2 and the 2nd As2S3 film 3 having 2.38 refractive index n1 are successively formed on a KCl substrate 4 having 1.45 refractive index ns after polishing both sides of the substrate optically and superprecisely. The resulting antireflection film has 0.015% absorption factor to CO2 laser light of 10.6thetam wavelength, and it can be used well even under 20kW high power irradiation. When the film is tested in the environment of 45 deg.C and 95% relative humidity, it is not damaged at all even after the passage of 650hr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a carbon dioxide gas laser beam (10.6 wavelength) that has low absorption and a wavelength of 0.6328 um,
Furthermore, the present invention relates to an antireflection film for potassium chloride that has excellent water resistance.

Conventionally, windows for high-power carbon dioxide lasers have the advantages of being transparent, having excellent water resistance, and producing large crystals, but have the disadvantages of being expensive and having to deal with optical problems when irradiating with high power. Large strain and toxic H during crystal growth
The use of 2re gas generates toxic selenium-based gas during the crystal surface polishing process, making it difficult to handle from a safety standpoint. GaAs is transparent at a wavelength of 10.6 μm, and its thermal conductivity is z.
Although it has the advantage of being about 3 times better than nSe and has excellent water resistance, it is not available with a diameter of about 8 crn or more, and the wavelength is 0.6328 for visible light superimposition.
It does not transmit μm He-Ne laser light, is expensive, has large optical distortion, and furthermore, arsenic (As
), which has many disadvantages such as the need for safety measures during cultivation and processing because it contains harmful elements.

On the other hand, KCI is a practical transparent optical component (window,
The main reason why it is not used as a substrate for lenses, etc.) is that it is deliquescent and dissolves in water, so it not only has the optical property of being transparent in humid environments μm, but also has water resistance. If possible, KCI windows and lenses with many of the advantages mentioned above could be realized.

Currently, there is no antireflection film that has both optical properties and water resistance at the same time.

An object of the present invention is to provide an antireflection film for Kcl that satisfies both optical properties and water resistance.

Currently, the antireflection coatings of KCl windows and lenses sold by Racer Power Optex Co., Ltd. of the United States are composed of a single layer of NaF. The refractive index of NaF is 123, which is very close to the square root of the refractive index of KCl (,/TT4-5 = 1.204), so the optical film thickness is nd-λ/4 = 2.6.
If a thickness of 5 μm is deposited, a reflectance of 0.05% can be expected, which is close to the ideal value. The reflectance of a KCI window having a diameter of 1 inch and five thicknesses with NaF antireflection coatings on both sides, which was actually purchased from the above-mentioned manufacturer, was measured at a wavelength of 10.6 μm. The conditions that must be met for the material of the anti-reflection film are that it is soluble in water.

A material must be selected that is transparent at wavelengths of 10.6 μm and 0.6328 μm, has good adhesion to the substrate, and exhibits an amorphous state that does not easily form pinholes when formed into a thin film. Therefore, promising materials include arsenic trisulfide (AS2S3) and sere7 trisulfide (As2Se3).
) and thorium tetrafluoride (ThF4).

Regarding the structure of the two-layer antireflection film, the following can be considered.

'f) KC1/GATS/A32S3'') KCl
/ A32S3/ ThF4c) KCI/ A32
ThF4 has a chalcogenide structure, but ThF4 is a radioactive substance and is legally prohibited in our country based on the above considerations.
Sandwiched with 32S3 for protection, and its three-layer film provides additional KC
The basic policy of the present invention is to protect I.

As for the effect, A 82 S 3 with less light absorption is KC
It has good adhesion to I and acts as a protective film against water. Furthermore, PbF2, which has low light absorption, is added on top of it, and its disadvantage of being vulnerable to water is further protected by A32S3, and the reflectance is zero. A high-power antireflection film that satisfies the requirements for an antireflection film and is also transparent to light with a wavelength of 0.6328 μm is realized. The present invention will be explained below with reference to Examples.

FIG. 1 is a structural diagram of a three-layer anti-reflection coating according to the present invention on a KCI substrate. 4 in the figure has ultra-precise light on both sides of 1.029μ
It is m. 3 has a refractive index n1 of 2.38.
16. No. 1 Op2722) was determined.

2, 3, and 4 show the first layer 1. Second layer 2
．． The setting value of the optical thickness n1dl of the third layer 3 is 1.02.
The second A S with a thickness of 9 μm and formed on the PbF2 film
2S'3 film, the optical thickness of the second A82S3 film is 1.08f1m ~
In the range of 1.154/jm, the reflectance at a wavelength of 10.6 μm was good at about 0.1%.

Figure 3 shows the case where the optical thickness of the first AS2S3 film on the KCI substrate is 2.617 μm, the optical thickness of the second A32S3 film is 1.120 μm, and the optical thickness of the PbF2 film is changed. The optical thickness of PbF2 film is 0.998μ
In the range of m to 1.060 μm, wavelength 10.6 μm
Good results were obtained with a reflectance of about 0.1%.

In Figure 4, the optical thicknesses of the PbF2 film and the second A S 2 S 3 film are 1.029 μm and 1.120 μm, respectively.
This figure shows how the reflectance changes depending on the optical thickness of the first A32S3 film when -m.
The optical thickness of the S3 film is 2.538 μm to 2.695 μm
In the range of , the total reflectance in the case of wavelength double-sided anti-reflection coating is about 0.8%, which is the practical limit.

As is clear from this figure, the optical thickness of the anti-reflection film for KCI according to this example is as follows:
．． 5384'm~2.695#m,, PbF2 film is 0
．． 998/Jm ~1.060/'r11. second A3
It is preferable that the 2S3 film has a thickness in the range of 1.086/Jm to 1.154 μm. I used a polished KCI substrate for sample preparation with a diameter of 1 inch and a thickness of 5 fi made by Janos Corporation in the United States. AS2S3
The evaporation crucible was made of molybdenum (MO) and had a lid with holes to prevent splashing, and the substrate temperature was 70℃ and the working pressure was 1.5℃.
X 10' Torr, deposition rate 12A0/SeC
It was deposited with PbFz was deposited using a platinum boat (Pt) at a substrate temperature of 118° C., a working pressure of 3XIQ'I'orr, and a deposition rate of 12A0/see. During deposition, the substrate rotated around its axis to ensure uniform film thickness. The deposition rate was controlled using a crystal oscillator, and the deposited film thickness was controlled using a transmission type optical film thickness control device using infrared light with a wavelength of 2.17 μm.

The transmittance spectrum of the obtained sample is shown in FIG. Actual value 0.12% in the wavelength range from 8 μm to 13 μm
, 0.23%, 0.18 coefficient, and the average value is 0.1
7% was obtained. The average absorption rate of the KCI substrate used is
Since it is on the order of 0.14%, if we take the difference between the two, the absorption rate of the antireflection coating on both sides is about 0.03%, and an antireflection coating with very low absorption rate was obtained. i.e. 20K
Even under irradiation with the high power laser beam of W, the power of the generated heat is 6
Since it is W, it can be used as an anti-reflection film for 20 KW.

Next, they conducted an experiment to determine the damage threshold of laser light irradiation.

The laser light irradiation damage value depends on the laser light irradiation conditions, that is, the relative size relationship between the laser beam diameter and the sample size, the method of cooling the sample, whether it is in air or vacuum, and the irradiation time. cannot be determined unambiguously.

Therefore, we set the following experimental conditions.

■ The irradiation experiment was conducted in air.

■ The sample was cooled by natural air.

■ The diameter of the sample is 1 inch, and the laser beam diameter is approximately 1 inch.
+Mn.

■ A 500 WCW carbon dioxide laser was used as the laser light source, and a Zn laser with a diameter of 1 inch and a focal length of 25 inches was used.
A single mode laser beam with a diameter of approximately 7 mm is focused using a 5e meniscus lens, and the energy density is 70KW/
After exposing the sample to c4 laser light for 2 minutes, the sample surface is observed and evaluated.

In the experimental results of the samples of the present invention under the above conditions, no change in the surface was observed before and after irradiation.

Finally, we will discuss the results of the moisture resistance test. , polished KC
As the relative humidity increases to 80 degrees or higher, I rapidly absorbs moisture and its weight increases. Therefore, the anti-reflection coating KCl
As a result of an accelerated test for moisture resistance against moisture, no damage to the anti-reflection coating was observed in the Ω sample of the present invention even after 650 hours. However, when water droplets are dropped on the antireflection film, the water has already seeped into the pinholes after one minute, and peeling of the film can be faintly observed. The above results show that under normal circumstances, if you are especially careful not to allow water to condense on the surface,
enumerate.

(1) The wavelength of the anti-reflection film is 10.6 μm.It is a practical anti-reflection film without carbon dioxide laser.

(3) Reduce the optical thickness of each of the three layers to 3% at the same time.
Even if it increases or decreases, the reflectance can be kept below 0.4 inches.

(4) Even when irradiated with a laser beam with an energy density of 70 KW/i for 2 minutes, the anti-reflection film will not be damaged in any way.

(5) Beam alignment is easy because it is transparent to He=Ne laser light with a wavelength of 0.6328 μm.

In summary, the present invention is based on potassium chloride (KCI)
``On at least one surface of the plate, a first arsenic trisulfide (A8
2S3) film, a lead fluoride (pbF2) film, and a second arsenic trisulfide (A82S3) film are formed in this order to provide an anti-reflection film for potassium chloride, which is also used for high-power carbon dioxide lasers of 20 KW. Optical properties

[Brief explanation of drawings]

A! ! Figure 3 shows the wavelength dependence of reflectance when the optical film thickness of 283 is increased or decreased by 3% from the set value. Figures 4 and 6 show the wavelength dependence of reflectance in various cases, and show the measured values and calculated transmittance spectra of a KCl window made by depositing the antireflection film of the present invention on both sides of a KCI substrate. This is a diagram showing a comparison of values. 1. First A32S3 film 2. ...PbF2
Vapor deposited film 3,... second A32S3 film 4,...K
CI board patent applicant Makoto Ishiita, Director of the Agency of Industrial Science and Technology Pa i (ζ1 person (〕1ml) Figure 6 i/! awe (Prrl)

Claims (1)

[Claims] (1) Potassium chloride (KCI) On at least one surface of the substrate, a tenth arsenic trisulfide (A82S3) film, a lead fluoride (pbFz) film, and a second arsenic trisulfide (As2S3) film are formed.
An antireflection film for potassium chloride, characterized in that the films are formed in this order. (2) First arsenic trisulfide (A82S3) film, lead fluoride (
PbF2) and the second arsenic trisulfide (As2S3) film have optical thickness values of 2.538 μm to 2.695 μm, respectively.
m. 0.998μm～1.060μm, 1.086μm
The antireflection film for potassium chloride according to claim 1, wherein the antireflection film is selected to have a thickness of 1.154 μm.